1. Field of the Invention
The present invention generally relates to information recording and/or playback devices and methods of positioning of magnetic heads of the devices, and more particularly, to an information recording and/or playback device and a method of positioning of a magnetic head of the device, in which the magnetic head is positioned by dual-stage actuators.
2. Description of the Related Art
There is great demand to improve the speed and accuracy of positioning a magnetic head of a magnetic disk device. Because of this, a magnetic disk device which has a dual-stage servo system comprising a slight movement actuator and a rough movement actuator is proposed.
For instance, a magnetic disk device having such the dual-stage servo system comprising a slight movement actuator and a rough movement actuator is described in Japanese Laid-Open Patent Application No. 11-031368.
A magnetic disk device having a dual-stage servo actuator will be described.
FIG. 1A is a plan view of the magnetic disk device having the dual-stage actuator. FIG. 1B is a vertical sectional-view taken on line Axe2x80x94A in FIG. 1A. FIG. 2 is a block diagram of the magnetic disk device having the dual-stage actuator.
The magnetic disk device 1 includes a disk enclosure 11 and a circuit board assembly 12.
The disk enclosure 11 has a case 21 and a cover 22. A magnetic disk 31, a spindle motor 32, a magnetic head 33, a suspension 34 and an arm 35, a slight movement actuator 36, and a rough movement actuator 37 are built in a space between the case 21 and the cover 22 of the disk enclosure 11.
The magnetic disk 31 is clamped to the spindle motor 32. The magnetic disk 31 rotates as the spindle motor 32 rotates. The spindle motor 32 is connected to the circuit board assembly 12 and rotates based on a driving signal provided by the circuit board assembly 12.
A magnetic head 33 is fixed on a head end part of the suspension 34. The magnetic head 33 faces the magnetic disk 31. The suspension 34 is provided on a head end part of the arm 35. The suspension 34 is capable of circular movement driven and in a disk radius direction (an arrow A direction). The suspension 34 and arm 35 are connected to each other by the slight movement actuator 36. The slight movement actuator 36, for example, is comprised of a shear type piezo actuator and makes the suspension 34 move circularly and in the arrow A direction. The other end part of the arm 35 is connected with the rough movement actuator 37. The rough movement actuator 37, for example, is comprised of a voice coil motor (VCM) and makes the arm 35 move circularly and in the arrow B direction.
The magnetic head 33 is connected to a flexible print wire board 38 by a print wire in the suspension 34 and the arm 35 or a lead line wired along the arms 34 and 35. A head IC 39 is mounted on the flexible print wire board 38. The head IC 39 is connected to the magnetic head 33. The head IC 39 amplifies a recording signal which is supplied to the magnetic head 33 and a playback signal which is played back by the magnetic head 33. In addition, the flexible print wire board 38 is connected with the slight movement actuator 36 and the rough movement actuator 37.
The head IC 39 is extended to a bottom surface side of the case 21 by the flexible print wire board 38, and connected to the circuit board assembly 12. The flexible print wire board 38 is connected to the spindle motor 32, the slight movement actuator 36, and the rough movement actuator 37. The flexible print wire board 38 is extended from an inside part of the case 21 to an outside part of a bottom surface of the case 21, that is, piercing the bottom surface.
The circuit board assembly 12 is provided at an outside part of the bottom surface of the case 21. Furthermore, the circuit board assembly 12 is connected to the flexible print wire board 38. The circuit board assembly 12 has a structure in which a hard disk controller (HDC) 41, a random access memory (RAM) 42, a read only memory (ROM) 43, a digital signal processor (DSP) 44, a micro processor unit (MPU) 47, a read channel (RDC) 45, and a servo controller (SVC) 46 are mounted on the print wire board 38.
The HDC 41 is connected to a high ranked controller 51, and thereby the HDC 41 controls a communication with the high ranked controller 51. The RAM 42 is used as a buffer memory in which data communicated with the high ranked controller 51 are stored temporarily. The RDC 45 modulates the recording signal recorded in the magnetic disk 31 and demodulates the playback signal played back from the magnetic disk 31, by the magnetic head 33.
The SVC 46 is connected to the spindle motor 32, the slight movement actuator 36, the rough movement actuator 37, and the DSP 44. The SVC 46 drives the spindle motor 32, as a relative speed of the magnetic head 33 and the magnetic disk 31 becomes a designated value based on the playback signal which is played back by the magnetic head 33. In addition, the SVC 46 controls the slight movement actuator 36 and the rough movement actuator 37 based on instructions from the MPU 44. And thereby, the magnetic head 33 follows a track formed in the magnetic disk 31.
The MPU 44 controls the HDC 41, the RDC 45, and the SVC 46 by firm ware stored permanently in the ROM 43, and thereby the MPU 44 controls an action of the whole of the device.
It is required for the slight movement actuator 36 of the above-mentioned dual-stage servo actuator of the magnetic disk device to have a high speed ability. Because of this, a shear type piezo actuator is used as the slight movement actuator 36.
FIG. 3 is a plan view of the dual-stage actuator in which the shear type piezo actuator is used as the slight movement actuator 36 and the VCM is used as the rough movement actuator 37. The piezo actuator has a movable area of xe2x80x9caxe2x80x9d(a plus direction of xe2x80x9caxe2x80x9d to a minus direction of xe2x80x9caxe2x80x9d) where xe2x80x9caxe2x80x9d is defined as a distance of 0.5 xcexcm from a center position of the movable area. The rough movement actuator 37 has a movable area of xe2x80x9cbxe2x80x9d (a plus direction of xe2x80x9cbxe2x80x9d to a minus direction of xe2x80x9cbxe2x80x9d) where xe2x80x9cbxe2x80x9d is defined as a distance of 12 mm from a center position of the movable area.
FIG. 4 is a view showing a frequency response of the piezo actuator namely the slight movement actuator 36. FIG. 5 is a view showing a frequency response of the VCM namely the rough movement actuator 37.
The piezo actuator has a main resonance frequency of 9 kHz, as shown in FIG. 4. On the other hand, the VCM has a main resonance frequency of 5 kHz, as shown in FIG. 5. Therefore, the piezo actuator can act with a higher speed than the VCM.
FIG. 6 is a block diagram of a track following control system of the dual-stage actuator.
At the time of track following, a tracking error signal is necessary. The tracking error signal represents a difference between an information of an objective position of the head and an information of a present position of the head. The tracking error signal is supplied to a controller 62 for controlling the slight movement actuator 36 and a controller 63 for controlling the rough movement actuator 37.
The controller 62 controls the slight movement actuator 36 based on the tracking error signal. The controller 63 controls the rough movement actuator 37 based on the tracking error signal.
The magnetic head 33 is moved a total amount by the slight movement actuator 36 and the rough movement actuator 37. A position of the magnetic head 33 is fed back as information providing a present head position. With the above-mentioned operation, the magnetic head 33 is positioned at the objective position.
FIG. 7 is a block diagram of a track seek control system of the dual-stage actuator.
As shown in FIG. 7, in this system, a control by the slight movement actuator 36 and a control by the rough movement actuator 37 are implemented separately at the time of a track seek. When a seek action in which the magnetic head moves a long distance is implemented, the rough movement actuator 37 makes the magnetic head move. Initially the slight movement actuator 36 is not under feed-back control but is fixed in a designated position. The slight movement actuator 36 starts moving in a latter settling action of the seek action. After a distance between the magnetic head and the objective track becomes so short that the distance is within the movable area of the slight movement actuator 36, the settling action is switched so as to use the slight movement actuator 36.
FIG. 8 is a view showing a wave form of a time response regarding the slight movement actuator, the rough movement actuator, and a head position, according to a conventional art. In FIG. 8, a position of the magnetic head 33 is expressed with a solid line, a driving position of the slight movement actuator 36 is expressed with a dashed line, and a driving position of the rough movement actuator 37 is expressed with an dash-dot line.
When a center of a movable area of the slight movement actuator 36 reaches an objective position 0 of the magnetic head 33 at a time of t0, it is possible to make the objective position 0, that is, move the magnetic head 33 to position 0, by using the slight movement actuator 36. Therefore, the action of the magnetic head 33 is changed from the seek action to the settling action. Since the slight movement actuator 36 is held at the center position of the movable area, the magnetic head 33 is positioned at a distance xe2x80x9caxe2x80x9d from the objective position 0 in a minus direction.
Once the settling action starts, the slight movement actuator 36 is driven. When the slight movement actuator 36 is shifted by xe2x80x9caxe2x80x9d from the objective position 0 to a plus direction as shown by the dashed line in FIG. 8, the magnetic head 33 is shifted to the objective position 0 in a short period of time. At this time, the rough movement actuator 37 is shifted to the objective position 0 as shown by the one point doted line in FIG. 8. The slight movement actuator 36 is shifted as the rough movement actuator 37 is shifted to make the magnetic head 33 stay at the objective position 0.
Accordingly, the magnetic head 33 can be set in an allowable deviation area where the objective position 0 is a center of the area, as shown by the solid line in FIG. 8. After the settling action is implemented, the track following action is implemented. For example, information recording and/or information playback action is implemented.
The seek action of the magnetic disk device 1 in which the dual-stage actuator servo system consisting of the slight movement actuator 36 and the rough movement actuator 37 is applied, for example, as described in xe2x80x9cMasahito Kobayashi, Takashi Yamaguchi, Roberto Horowitz, xe2x80x9cTrack-Seeking Controller Design for Dual-Stage Actuator in Magnetic Disk Drivesxe2x80x9d, Proceedings of the American Control Conference, Chicago, Ill., June 2000xe2x80x9d.
A seek action over a short distance is mainly described in the above-mentioned reference. According to the reference, a response to an action in a range exceeding the movable area of the slight movement actuator 36 is improved by a switching means. The switching means allows a control loop of the slight movement actuator 36 and the rough movement actuator 37 to avoid mutual interference and switches respective objective paths at the time of a full operation of the slight movement actuator 36 and the rough movement actuator 37.
If the limitation of the movable area of the slight movement actuator 36 in the settling action of the magnetic disk device having a conventional dual-stage actuator is eased, it may be possible to switch the settling action at an earlier time than t0 shown in FIG. 8. As a result of this, the seek action can be implemented in a shorter period of time. Although a response at the time of settling action is improved under the limitation of the movable area of the slight movement actuator 36, the limitation of the movable area itself is not eased, in a method in the above-mentioned reference.
In order to ease the movable area limitation of the slight movement actuator in the settling action of the magnetic disk device having a conventional dual-stage actuator, it is necessary to solve a difficult problem. That is, it is necessary to expand a range of a driving voltage, or reduce a rigidity of the actuator by making sacrifices to a resonance property of the slight movement actuator 36.
Accordingly, it is a general object of the present invention to provide a novel and useful information recording and/or playback device method in which positioning of a magnetic head of the information recording and/or playback device is implemented in a short period of time, where one or more of the problems described above are eliminated.
Another and more specific object of the present invention is to provide a disk device including a head part, an actuator part for moving the head part to an objective position, and a control part for controlling the actuator part, wherein the control part makes the actuator part shift to a reverse direction of the movement direction of the head part before a settling action of the head part starts being implemented.
According to the above invention, from a starting time of a seek action to the settling action, the head such as a magnetic head is shifted to a reverse direction of a current direction of a movement of the head. Therefore, it is possible to start implementing the settling action at an earlier timing than the conventional art, and thereby the head can be set at the objective position in a short period of time. Hence, the seek action is implemented quickly.
In the above-mentioned device, the actuator part may comprise a slight movement actuator for a slight movement of the head part and a rough movement actuator for a rough movement of the head part. In addition, an objective position of the slight movement actuator may be shifted to a movement direction of the head part and an objective position of the rough movement actuator may be shifted to a reverse direction of the movement direction of the head part before a settling action of the head part starts being implemented.
According to the above invention, the settling action, by which the magnetic head is set at the objective position, is implemented before the magnetic head reaches the actual objective position. And thereby, the seek action is implemented quickly.
Other objects, features, and advantages of the present invention will be more apparent from the following detailed description when read in conjunction with the accompanying drawings.